A dryer vent is a short 4-inch metal pipe that goes from the back of the dryer to the wall ductwork in the house. It is essential to have because it exhausts the moisture from the dryer out of the house. Without it the moisture gets trapped in the walls and attic which promotes mold and mildew. It also prevents the dryer from working effectively because it has to work much harder to blow the hot, moist air out of the house. This can burn out the dryer motor.
Dryer vents come in different sizes and materials. The most affordable are the flexible vinyl or plastic hoses that attach to the back of the dryer. They are cheap and easy to install but they are the worst offenders when it comes to lint buildup and fire hazards. They also kink easily and can be crushed or obstructed by other objects in the home. They should be replaced with semi-rigid aluminum or rigid metal ductwork.
Rigid metal duct is the best option because it has a smooth interior which encourages air and lint to move freely through the duct. It is usually made of aluminum but may be galvanized steel in older homes. It is the only type of duct that can be installed inside a wall or other enclosed space, although it can be used with short lengths of flexible transition tubing for connections to other ducts. It is often paired with slim ducts (also called periscope ducts) in houses with tight locations where a regular rigid duct is not possible or desired.
The slim duct, which is actually a telescoping rigid aluminum tube with a round collar on each end, can be used as a short section of transition duct or for connecting to a vent in an extremely tight location. It is generally not used for the entire dryer vent run because it can be difficult to get enough air flow through it. The flexible tubing that connects it to the dryer and other ductwork should be a minimum of 2 inches in diameter.
It is important for dryer ducts to be properly constructed and maintained. They should be at least 4 inches in diameter, have a smooth interior and not be connected with screws or similar fasteners that can accumulate lint. They should also be vented to the exterior of the house and not into attics or other enclosed areas, which can become breeding grounds for molds.
If your home inspector notices that a duct is improperly constructed or dirty, they may recommend professional dryer vent cleaning. These professionals disconnect the dryer from the vent hose and then use the appropriate tool to clean out the inside of the duct and the hose until it is squeaky clean. They may blow, brush, vacuum or dismantle it as needed to clean the entire length of ductwork that is being vented from your house. It is recommended that you have your dryer vent cleaned at least once a year.